The original is the best, in my humble opinion.

And Origins mimics the nes version, so Origins is definitely the better pick.

DoS is so easy, with different number systems and cahracter attributes and new levels and so on that it's hard to call it FF1. It's more like a game based on FF1 Origins, which is based on Final Fantasy, which is an old nes game.

So buy friggin' Origins and play it. If you want to play a cheap game that's very similar, then check out DoS.

Especially since FF2 is pretty cool.